The present invention is generally directed to an apparatus and method for providing a single-size register grill system. In one aspect, a grill system which can be adapted for use with multiple sizes of register boxes is provided. The grill system includes a grill funnel configured to be attached to a register box, the grill funnel having a body with an airflow pathway that includes an airflow opening and a plurality of secondary airflow openings, wherein the secondary airflow openings are initially closed. The grill system further includes a grill assembly having a plurality of airflow adjustment members for controlling the airflow through the airflow pathway, wherein the grill assembly is attached to the grill funnel. In another aspect, a method of using a grill system is provided. In yet a further aspect, a grill funnel for use with a register box and a grill is provided.